A polyarylene sulfide (hereinafter sometimes abbreviated to as “PAS”), especially polyphenylene sulfide (hereinafter sometimes abbreviated to as “PPS”) is known as an engineering plastic which is excellent in mechanical strength and heat resistance and the like and which has good electrical characteristics and high rigidity. Thus it is widely employed as a variety of materials such as electronic parts, electrical parts and mechanical parts. In particular, a molded article of a resin composition composed of polyphenylene sulfide and an inorganic filler is employed for a variety of purposes of use.
With regard to a conventional process for the production of a PAS by reacting a dihalogenated aromatic compound such as p-dichlorobenzene with an alkali metal sulfide such as sodium sulfide and lithium sulfide in the an aprotic organic polar solvent such as N-methyl-2-pyrrolidone (NMP), a prescribed amount of water is added to the process, since the alkali metal sulfide is insoluble in a polar solvent. In this case, the alkali metal sulfide is dissolved in a polar solvent in the presence of water, and a part thereof is turned into an alkali metal hydrosulfide by hydrolysis. The alkali metal hydrosulfide thus formed suppresses the improvement in the molecular weight of a PAS, turns a terminal of a polymer into —SH group, thereby having caused such problems as the production of a PAS having inferior thermal stability.
In order to solve the above-mentioned problems, there are proposed a method for imparting a high molecular weight to a PAS which comprises adding water to reactants, and thereafter carrying out preliminary polymerization at a low temperature {refer to Japanese Patent Application Laid-Open No. 9228/1989 (Showa 64)}, a method which comprises carrying out preliminary polymerization by adding a small amount of water to reactants so as to increase the conversion of an alkali metal sulfide, and thereafter carrying out polycondensation by adding water to the reactants {refer to Japanese Patent Application Laid-Open No. 7332/1986 (Showa 61)} and the like.
However, any and all of the aforesaid methods still remain unsatisfactory in regard to the obtainment of a PAS which has a high molecular weight and is excellent in thermal stability.